A number of different types of equipment may be used efficiently to carry telephone signal traffic by combining or "multiplexing" the signals from several telephone lines and transmitting the signals at a faster rate over a single, high-speed line. These devices accept a number of different voice or data signals at a low bandwidth and produce a time division multiplexed output signal, typically in digitized form, having a higher bandwidth. For example, one commonly used signal format for digital multiplex transmission is known as a T1 span.
Multiplexed signaling is of particular interest to businesses and other high volume customers of telephone services. For example, interexchange carriers (IXCs), such as AT&T, MCI, and Sprint, offer their customers favorable tariffs for subscribing to various types of digital multiplex services that utilize a multiplexed line such as a T1 span. In a typical configuration, the customer sends signals over so-called DS0 or sub-DS0 rate telephone lines to the input ports of a multiplexer located, for example, at a central office of the local telephone service provider. The multiplexer combines the signals on these relatively low bandwidth incoming lines, by time division multiplexing, and provides a multiplexed output signal. It then sends this output signal over one or more high bandwidth connections, such as a T1 span, to the public switched telephone network, a data network, or leased lines. These multiplexed signals may be voice or data, and may include DS1, DS3, packet data, frame relay, or video signals.
The various types of multiplexer devices in current use include integrated access devices (IADs), channel banks, and digital access cross-connect systems (DACS). Each of these multiplexer devices handle both voice band and data signals. The channel banks are typically used for voice band signal multiplexing, IAD devices for a mix of voice band and data signal traffic, and DACS for "nailed up" voice band or data services.
Each of the multiplexer devices connect a number of distinct, physical lines to specific network services. For example, the device may connect one-third of the lines from the customer equipment to network lines that send and receive voice rate signals, some locally and some long distance, and two-thirds of the lines to network lines that handle the faster data transfers. These devices make efficient use of the network services by sending to them appropriate signals from the customer equipment. By selectively connecting equipment on the customer's premises to lines that are routed through one of these devices to the particular network services, the customer can essentially configure how outbound traffic from its equipment is applied to the network. For example, the customer may connect its telephones to lines that connect, through an IAD, to a network of voice rate lines and its modems and facsimile machines to lines that connect, through the IAD, to a network of data rate lines.
The multiplexing devices may be installed at the central office of a telephone service provider, as discussed above, or they may be installed at a customer's premises, to service that customer and/or a number of customers in the same building or complex of buildings. These end office devices are, however, typically owned and controlled by the service provider.
In order to change the configuration of the multiplexing device, that is, to connect a given subset of the customer's lines to different types of network services, the multiplexing equipment must be reprogrammed. This typically requires that the customer notify the service provider, and the service provider perform the re-programming to provision the requested service. Such a reconfiguration may even require the installation of new hardware at the service provider's central office, for example, to increase the number of lines that ultimately connect to the network data services. Accordingly, such changes to the device's configuration are not immediate and may be quite costly.
Changing the mix of voice and data connections at the IAD solves one problem, it connects selected customer equipment to established connections to network services. It does not, however, address the problem of changing the connections between the IAD and the various network services.
Unless the customer is willing to pay the cost of a permanent, or "nailed-up" connection through the central office of the local service provider, the customer's access to the network is typically made through a switch in the central office. The switch makes an association between the physical ports, or lines, coming from the IAD on the slow customer side and time slots associated with the high speed, network side. Thus, there is a "mapping" of the switch input ports to time slots. This mapping is essentially programmable, so that it can accommodate changes to a customer's service contract, i.e., the addition or deletion of network services from that contract. However, in prior known systems, this re-programming involves manual manipulation of the switch connections. The reconfiguration is thus both costly and time consuming.
The way that telephone systems have evolved over time, a customer is typically constrained to consolidating its voice traffic onto a Private Branch Exchange (PBX) or "legacy" system, and its data traffic onto one or more data networks dedicated to handling data services. Accordingly, the customer is paying for the two or more different types of independent connections into the PSTN and/or other telephone networks, although not all of the available capacity of any of these connections may be used all of the time.
For example, during the day a business customer may require a certain number of DS0 or sub-DS0 rate lines for voice traffic. At night, these voice lines are typically idle, and the customer may need instead to use high-speed data services, to transfer data, such as the day's sales receipts, to another location. This customer must thus maintain the unused voice line connections during the night and the unused data line connections during the day. One option is switched services, but this can be expensive for high rate data services. What is needed is a switching device that can be dynamically reconfigured to assign appropriate network connections, i.e., voice or data network connections, to lines originating from the customer equipment.
The customer may also temporarily require extra bandwidth at various times. For example, the customer may desire to hold a video teleconference, which requires the concurrent use of several lines. To handle such teleconferences using prior known systems, the service providers allow a customer, by prior arrangement, to request that several lines be essentially tied, or "bonded," together. During the pre-arranged conference the service provider connects the customer to the requisite number of lines through the switch. If the customer exceeds the allotted bandwidth, the service provider typically does not accommodate the excess signal traffic and signals may be lost. Further, the bonding service is only available at the pre-arranged times. These systems thus can not accommodate unscheduled or impromptu teleconferences. What is needed is a switch that dynamically allocates to the customer lines, as needed, appropriate bandwidth, i.e., an appropriate number of time slots.